1. Field
Apparatuses and methods consistent with exemplary embodiments relate to wide dynamic range (WDR) image processing.
2. Description of the Related Art
A wide dynamic range (WDR) is also referred to as a high dynamic range (HDR) but, hereinafter, is referred to as a WDR.
Recently, a WDR photographing function is increasingly used. The WDR photographing function is used to obtain an image in a dynamic range that exceeds a dynamic range within which an image sensor may capture an image, by sequentially photographing and synthesizing a short time-exposed image (hereinafter referred to as “a short-exposed image”) and a long time-exposed image (hereinafter referred to as “a long-exposed image”). The WDR photographing function has a remarkable effect in an environment in which a contrast ratio is very high, such as an environment with backlight.
However, there are two problems that may be caused, with regard to a structure for synthesizing a short-exposed image with a long-exposed image. One problem is that, in synthesizing, an object in motion may cause deviation of contours of the object, and thus, an artifact in which a contour of the object may be doubled in an image. The other problem is that, if a flicker is photographed in a short-expose image and when the short-exposed image is used in synthesizing, a synthesized image that includes the flicker may be output. Thus, the image may not be clear. The inventive concept is provided mainly to address the other problem that relates to a flicker.
An example, in which a flicker is generated, may be a fluorescent lamp that does not include an inverter. Some light-emitting diode (LED) lighting, which has been supplied recently, has a low flickering frequency, and such low frequency flickering may still cause generation of a flicker. Additionally, a TV apparatus that includes a liquid-crystal display (LCD), or a display that is used for a personal computer (PC) increasingly employ flickering of backlight, so as to improve performance of a video display. The flickering of backlight may also cause generation of a flicker.
Hereinafter, methods of mitigating a flicker with regard to a WDR are described. One method is mainly to correct a difference between a white balance (WB) that is generated when images, which are photographed in an environment with a flashlight, are synthesized and a WB that is generated when images, which are photographed in an environment without a flashlight, are synthesized (refer to Japanese Patent Registration No. 2011-35894). In this case, a flicker may be reduced by weighted-averaging of several images. A WDR effect may also be obtained by weighted-averaging of several images. Additionally, a gain may be adjusted to correct a WB.
The other method is performed by comparing an image that is photographed with a shutter speed of 1/240 second to an image that is photographed with a shutter speed of 1/60 second, so as to detect a flicker (refer to Japanese Patent Registration No. 2012-119761). In this case, a priority is set respectively for several WDR synthesized images and a tone-compensated image that is obtained from a short-exposed image. Then, based on the corresponding priority, display or recording of the several WDR-synthesized images and the tone-compensated image that is obtained from the short-exposed image is controlled. If a flicker is detected, a combination ratio of the tone-compensated image, instead of the WDR synthesized images, may be raised.
However, the method, disclosed in Japanese Patent Registration No. 2011-35894, may have a less WDR effect, compared to a type of synthesizing a short-exposed image with a long-exposed image. Additionally, with regard to the method, disclosed in Japanese Patent Registration No. 2011-35894, since several images are weighted-averaged, frame memories, in correspondence with the number of frames, are needed, a memory size or a data transmission load may be increased. A motion detection result is employed for calculating a gain for adjusting the WB. However, a problem, in which a contour of an object in motion may be doubled due to weighted-averaging of several images, may not be solved.
With regard to the other method that is disclosed in Japanese Patent Registration No. 2012-119761, reference images for flicker determination need to be acquired before photographing. Additionally, while a moving image is photographed, if there is a change in whether a flicker is present or not, such a change may not be properly processed. If a flicker is detected by using the other method that is disclosed in Japanese Patent Registration No. 2012-119761, a combination ratio of a tone-compensated image, instead of the WDR synthesized images, may be raised. Thus, a WDR effect may remarkably deteriorate.